As described in EP345856, alkylene oxides may be prepared by contacting an alkyl phenyl hydroperoxide with an alkene to obtain an alkylene oxide and an alkyl phenyl alcohol. The alkyl phenyl alcohol may then be converted by dehydration into the corresponding aromatic alkene.
The afore-mentioned epoxidation and dehydration processes are typically employed in the co-production of propylene oxide and styrene from ethyl benzene hydroperoxide and propylene.
Alkyl phenyl hydroperoxides used in such epoxidation reactions may be prepared by reacting an alkyl aryl compound and oxygen to produce a reaction mixture comprising alkyl phenyl hydroperoxide, alkyl aryl compound and oxygen. The reaction mixture may be separated into a liquid phase comprising alkyl phenyl hydroperoxide, and a vapour phase comprising alkyl aryl compound and oxygen. The liquid phase comprising the desired alkyl phenyl hydroperoxide product may then be used in the preparation of the alkylene oxide. The vapour phase comprising alkyl aryl compound and oxygen may be condensed, and the condensate at least partly recycled to prepare further alkyl phenyl hydroperoxide.
If the oxidation of the alkyl aryl compound proceeds with low selectivity, then the reaction may also produce by-products such alkyl phenyl alcohol and alkyl phenyl ketone.
Besides the desired alkyl phenyl hydroperoxide and the afore-mentioned by-products, a wide range of additional contaminants are created during the oxidation of alkyl aryl compounds. Although most of these contaminants are present in small amounts, the presence of the organic acids especially has been found to cause problems in the further use of the alkyl phenyl hydroperoxide in epoxidation. It is therefore known to contact the liquid phase of the reaction mixture with aqueous base in an amount sufficient to neutralize acidic components, e.g. as described in WO2004076408. Subsequently the resulting mixture can be phase-separated into separate aqueous and organic (hydrocarbonaceous) phases. The organic phase, which contains some base, can then be water washed to further separate the basic materials, e.g. as described in WO2007116046.
In circumstances wherein it is desirable to co-produce alkylene oxides and aromatic alkenes, then it is possible to convert alkyl phenyl alcohol and alkyl phenyl ketone by-products resulting from the oxidation of alkyl aryl compounds into their corresponding aromatic alkenes, thereby increasing the overall yield of aromatic alkene from the integrated process to produce alkylene oxide and aromatic alkene.
However, there are times when market conditions do not favour the co-production of aromatic alkenes along with alkylene oxide. Under such circumstances it is desirable to minimise the amount of alkyl phenyl alcohol and alkyl phenyl ketone co-produced during the oxidation of alkyl aryl compound. That is to say, by improving the selectivity of the alkyl aryl compound oxidation to the corresponding alkyl phenyl hydroperoxide, it becomes possible to produce more alkylene oxide for every molecule of co-produced aromatic alkene.
Furthermore, it is desirable to improve the selectivity of alkyl aryl compound oxidation to the corresponding alkyl phenyl hydroperoxide in order to reduce the formation of certain undesirable contaminants that also reduce the overall feedstock yield. That is to say, by improving the selectivity of the alkyl aryl compound oxidation to the corresponding alkyl phenyl hydroperoxide, it becomes possible to lower the overall consumption of alkyl aryl compound for every molecule of alkylene oxide produced.
For example, with regard to the co-production of propylene oxide and styrene from ethyl benzene hydroperoxide, formation of 1-phenylethanol and acetophenone during the oxidation of ethylbenzene will increase the overall production of styrene vis-à-vis propylene oxide in an integrated process. However, in times when market demand for styrene is low, it is preferable to minimise formation of such by-products in order to be able to increase the production of propylene oxide for every molecule of co-produced styrene.
In the preparation of ethyl benzene hydroperoxide according to the above general process on an industrial scale, a drop in selectivity has been observed over a prolonged time, as a creeping trend. However, for the reasons described above, a high selectivity of the oxidation reaction is of importance in an industrial context in the manufacture of alkylene oxide. Thus, even small losses in selectivity during the afore-mentioned oxidation reaction can have a major impact on the economy of production of alkylene oxide therefrom. Moreover, the smaller amounts of by-products that cannot be converted into either propylene oxide or styrene which are formed during the oxidation step need to be minimized at any time in order to maximize the overall economics of the process.
It is an object of the invention to address selectivity drops during the preparation of alkyl phenyl hydroperoxide from alkyl aryl compound and oxygen, thereby improving the overall selectivity of a process for preparing an alkylene oxide by preparing producing more alkylene oxide for every molecule of co-produced aromatic alkene and minimizing the amount of waste.